But the dense gray haze hanging over the Asian capital and many other parts of that nation is not simply reason for local anxiety.

Industrial pollutants from China's increasingly robust use of coal are plating out across the globe, including here in Alaska, brought here by storms crossing the Pacific Ocean transporting tons of airborne chemicals that shower onto coastal waters and inland where it they end up in the local food chain, according to scientists studying the phenomenon.

"We see the Chinese influence every spring and summer," said Prof. Cathy Cahill, a faculty member of the Chemistry Department at the University of Alaska Fairbanks, who has been studying the international transport of pollutants for 22 years, 10 of them in Alaska.

During those months, Cahill explained, storms tend to move fast, allowing particulate matter little time to precipitate during the journey from Asia. Thus, more of it reaches Alaska.

Scientists have developed methods for proving where pollutants are generated by identifying their chemical signatures and by tracing meteorological data, She said. For instance, dust storms originating in the Gobi Desert during March and April blow across the Pacific and Bering Sea to Alaska. Depending on the wind patterns in Asia, those dust storms may first head southeast over China or northeast over Siberia, as well as over Korea and Japan, all the while accumulating pollutants in the dust.

"The dust helps us say definitively that pollution is coming from China," Cahill said.

China's industrial push

Much of China's air pollution is generated by coal-fired power plants, which produce three out of every four watts of electricity used in the country. Adding to the problems are coal-burning factories so numerous some estimates put their combined labor force at more than 100 million. Home stoves contribute still more coal-generated pollution.

The nation's ambitious industrialization effort is compounding the problem, adding a new coal-fired power plant to the energy grid at an average rate of one a week.

The Olympics have led Chinese officials to slow down production in some factories, close others around venues in Beijing, and pull million of vehicles off city roads, according to an Associated Press story published Thursday.

But power plants can't easily be shut down, Cahill said.

Particulate is the problem

Of major concern is particulate matter smaller than 2.5 microns, which is about a fiftieth the diameter of a human hair and thus small enough to breach the inner defenses of noses and enter into lungs. The day before opening the ceremonies were to begin, Beijing air reportedly registered 374 micrograms per cubic meter.

"The U.S. air quality standard is 15 micrograms per cubic meter," said Cahill, who visited Beijing and other Chinese cities in 2004.

"It's bad. If you're educated, you probably live in an urban area. But your life expectancy in the city is 58 years. It's 72 in the countryside," she said.

A Scientific American article published online this week noted that a brown cloud leaving China is visible from space "and takes about a week to cross the Pacific to the western U.S., where it accounts for as much as 15 percent of the air pollution."

"Alaska, unfortunately, is stuck," Cahill said. "We are downwind."

Unless international diplomatic pressure on the Chinese government succeeds in encouraging further efforts to control pollution, there is little Alaska can do, she said.

While carbon dioxide, a greenhouse gas, is a major component of air pollution out of China, Cahill's studies concentrate on particulate, including mercury, sulfur and nitrates.

"They're bad actors," she said, adding that they produce acid rain and are harmful to lungs. "By the time they get to us, a lot of it has fallen out. Our concentrations are low, but it is the long-term deposition we are concerned about. Even a little bit of mercury over a long period of time becomes significant."

When elemental mercury in the air comes in contact with water, biological processes can turn it into methyl mercury, hazardous in part because it bio-accumulates, especially in fatty tissues. Fish are particularly vulnerable.

The Arctic Monitoring and Assessment Programme, one of five working groups of the Arctic Council, advises the United States and seven other arctic nations on pollution threats to the region. Studies by the AMAP show contaminants arriving via long-range transport, as well as those from local sources, accumulate in traditional foods, often at levels exceeding foods from outside the arctic.

The AMAP reported that cadmium and mercury tend to accumulate in marine food webs.

"Methyl-mercury is efficiently taken up following consumption and poses the main potential risk," the AMAP said.

Cahill said mercury transfers to fetuses through umbilical cords. The AMAP reported that average umbilical cord blood levels of methyl-mercury were "two- to ten-fold higher in newborns in the arctic region than in newborns from regions farther south."

A six-year study by the Western Airborne Contaminants Assessment Project released in February said, the "biological effects of airborne contaminants include impacts on reproductive success, growth, behavior, disease and survival. Subsistence hunters and gatherers in Alaska depend on wild food sources that may be affected by airborne contaminants."

The results of mercury testing conducted on Alaska species between 2001 and 2006 led the Alaska Department of Health and Social Services and the Department of Environmental Conservation to issue fish-consumption guidelines last fall.

Though noting, "the health benefits of eating fish far outweigh any potential risk," the agencies nevertheless recommended limiting consumption of five species of sport-caught fish

For instance, the department said yelloweye rockfish, large lingcod (40-45 inches) and large halibut (50-90 pounds) could be eaten as often as twice a week, but salmon shark, spiny dogfish, and very large lingcod over 45 inches and large halibut weighing over 90 pounds should be eaten only as often as once a week.

Most commercially caught halibut weigh an average of 33 pounds and can be safely consumed up to four times a week. Small halibut and wild Alaska salmon were lower in mercury content, the state said.

The Alaska Department of Fish and Game continues to collect and test fish for environmental contaminants, and consumption guidelines are periodically updated. More information is available on the state's Web site.

State's air is mostly clean

By and large, the air outside Alaska's major cities remains considerably cleaner than in other parts of the United States, as is shown by measurements taken in Denali National Park since 1986 (making it one of the oldest running monitoring sites in the country). The fact that air there is so pure makes determining the sources of airborne pollution reaching Alaska relatively easy, Cahill said.

More of China's pollution reaches Oregon and California daily than reaches Alaska, primarily because of the jet stream across the Pacific, Cahill said. But warmer temperatures there keep can the chemistry volatile at lower latitudes.

In a process Cahill called "the grasshopper effect," pollutants condensing out in lower latitudes often get airborne again, skipping their way on the winds toward the arctic, where they accumulate much more permanently in the cold ground and waters -- eventually getting into things we eat.

It is simply a matter of physics that pollution generated by burning coal in such prodigious quantities in China reaches the North American continent. Pacific winds waft eastward toward North America.

Coal may add to the problem

Ironically, Alaska mining and export policy could one day contribute to the rain of mercury and other particulates falling on state coastal waters and land. Alaska boasts one of the richest deposits of untapped coal in the world, and there are companies eyeing the exploding Asian demand and seeing an exploitable market hungry to import. One possible source of that coal lies only miles from the Kenai Peninsula.

PacRim Coal LLP, owner of the Chuitna project, holds a lease on 20,571 acres of land northwest of Tyonek thought to contain an estimated 1 billion tons of ultra-low sulfur, sub-bituminous coal. The company hopes eventually to mine that deposit over the course of several decades, with most of it going to Pacific Rim customers. Some could fuel electrical generating plants in Alaska.

Last year, Judy Heilman, of the Chuitna Citizens NO-COALition, said every study showed the main source of mercury in Alaska fish was Asia.

"So why is the state moving forward to destroy fish and game habitat in our backyard with a huge strip mine and compounding the problem by putting our fish at risk of more mercury from coal?"

Cook Inletkeeper Director Bob Shavelson said in the same press release that Alaskans consume a lot of fish, "and mercury contamination from coal is not compatible with smart fish management."